Gun going through floor when dropping?

hi, i made a gun system but when i drop a gun it falls through the terrain. anything i need to explain further ill be around, heres my code, however im not sure it has to do with my code. ill also leave my project for people to have a peek.

using UnityEngine;
using System.Collections;

public class Gun : MonoBehaviour {

	public GameObject Weapon1Get;
	public GameObject Weapon2Get;
	private GameObject WeaponDropped;

	void OnMouseDown () {
		Debug.Log ("YES");
		WeaponDropped = Weapon1Get.GetComponent <Weapon1> ().CurrentWeapon;
		WeaponDropped.collider.enabled = true;
		WeaponDropped.rigidbody.detectCollisions = true;
		collider.enabled = false;
		rigidbody.detectCollisions = false;
		Weapon1Get.GetComponent <Weapon1> ().CurrentWeapon = gameObject;

	void OnCollisionEnter (Collision Col)
		if (Col.gameObject.tag == "Player")
			Physics.IgnoreCollision (collider, Col.gameObject.collider);

Try Weapon1Get.collider.enabled = true and Weapon1Get.rigidbody.detectCollisions = true; Instead what you’ve already written.